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DIGITAL ELECTRONICS
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Introduction to Digital Electronics
Digital Electronics represents information (0, 1) with onlytwo discrete values.
Ideally
“no voltage (e.g., 0v) represents a 0 and
“full source voltage (e.g., !v) represents a 1"ealistically
“low voltage (e.g., #1v) represents a 0 and
“high voltage (e.g., $%v) represents a 1
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What is a Digital System?Digital system&ystem that ta'es in digital inputs and generates digital
outputsEample *omputer
Digital inputs (letters and num+ers from 'ey+oard)Digital output (new num+ers or letters stored to a file or display
on screen)
any other digital systems eist*ell phones, automo+ile control engines, - set top +oes,
musical instruments, DD players, digital cameras, finger printrecognition, …
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Analog versus Digital
/nalog systems process timevarying signals that canta'e on any value across a continuous range of voltages
(in electricalelectronics systems).
Digital systems process timevarying signals that can
ta'e on only one of two discrete values of voltages (inelectricalelectronics systems).Discrete values are called 1 and 0 (23 and 244, 5I65
and 728, -"9E and 4/7&E, etc.)
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Digital vs. Analog
Digital signalDiscrete
&ignal that can have one of a finite set of possi+le values
/nalog signal*ontinuous
&ignal that can have one of an infinite num+er of
possi+le values
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Analog versus Digital
A digital signal,unlike continuousanalogue signal,varies abrutl! andc"anges bet#eendistinct voltage orcurrent levels$
%co&&onl! t"e ' or (voltage levels o) abinar! s!ste&*
analoguesignal
digital signal
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Binary Digits and Logic Levels
Digital electronics uses circuits thathave two states, which are represented
+y two different voltage levels called
5I65 and 728. -he voltagesrepresent num+ers in the +inary system
In +inary, a single num+er is called abit (for binary digit ). / +it can have thevalue of either a 0 or a 1, depending onif the voltage is 5I65 or 728
5I65
728
V 5(ma)
V 5(min)
V 7(ma)
V 7(min)
Invalid
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Digital WaveformsDigital waveforms change +etween the 728 and 5I65
levels. / positive going pulse is one that goes from a
normally 728 logic level to a 5I65 level and then +ac'
again. Digital waveforms are made up of a series of
pulses
4alling or
leading edge
(+) 3egative:going pulse
5I65
"ising or
trailing edge
728
(a) ;ositive:going pulse
5I65
"ising or
leading edge
4alling or
trailing edge
728t 0
t 1
t 0
t 1
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Advantages of Digital Systems
1. Digital systems are generally easier to design
. ore digital circuitry can +e fa+ricated on I* chips
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Limitation of Digital Systems
Digital signal will not +e an eact copy of the original
analogue signal sampling error
-o ta'e advantages of digital techni?ues*onvert analog inputs to digital
;rocess the digital
*onvert the digital outputs to analog
@oth analog and digital techni?ue can +e employed inthe same system called hybrid system
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Integrated Circuits
I* is an electronic circuit, *onstructed entirely on a single piece of semiconductor material called su+strate ,referred
as a chip.
*lassification of I* /nalog A Digital
Digital IC are collection of resistors, diodes and transistorfa+ricated on a single chip.
3o additional component re?uired for their operation.
2; : logic level 0 or 1.
7ow cost ,low power, smaller siBe./nalog I*s, such as sensors and operational amplifier,
wor' +y processing continuous signals
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+reared b! $T$ NG(-
Integrated Circuits
/ gate is a physical implementation of a @ooleanfunction
7ogic gates are usually em+edded in Integrated*ircuits I*s, sometimes referred as *hips
/ccording to its compleity, I*s are classified as&&I, &I, 7&I and 7&I ( small, medium, l arge Avery l arge scale integration)
7ogic gates I*s may +e *2& type, +oth re?uirea power supply of C! volts and a ground in
addition to the logic inputs DI; type (dualinline pac'age) logic I*s will +eused in our eperiments
1
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=
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F
1%
1=
1<
11
10
G
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.cc
63D
Top view of a logic gate IC
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Levels of Integration
Digital I* are *ategoriBed according to their circuit
*ompleity.num+er of e?uivalent logic gates on thesu+strate.
&mall &cale Integration or (&&I) *ontain up to 10
transistors or a few gates within a single pac'age such as
/3D, 2", 32- gates.edium &cale Integration or (&I) +etween 10 and 100
transistors or tens of gates within a single pac'age and
perform digital operations such as adders, decoders,
counters, flipflops and multipleers.
7arge &cale Integration or (7&I) +etween 100 and 1,000
transistors or hundreds of gates and perform specific digital
operations such as I2 chips, memory, arithmetic and logic
units.
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Levels of Integration contd..!
ery7arge &cale Integration or (7&I) +etween 1,000 and10,000 transistors or thousands of gates and perform
computational operations such as processors, large memory
arrays and programma+le logic devices.
&uper7arge &cale Integration or (&7&I) +etween 10,000and 100,000 transistors within a single pac'age and perform
computational operations such as microprocessor chips,
microcontrollers, +asic ;I*s and calculators.
9ltra7arge &cale Integration or (97&I) more than 1million transistors the +ig +oys that are used in computers
*;9s, 6;9s, video processors, microcontrollers, 4;6/s
and comple ;I*s.